Hey Autumn.....

whenever I feel I need some chin work, I do about 40 repititions of tilting my head back slightly...until I feel a little tightening of the front of my neck, then I extend my lower jaw forward and then up as far as I can....as you move through the motion, you should feel the strain in your "double-chin" area........I usually do about 40 reps, and always feel sore the next day, and a little tighter under the chin......

I don't know about proven....but it seems to work for me.....I don't have a regular schedule that I follow, I just do them when I think of it......and nobody's watching

.....I'm a ssuming that this motion doesn't have any negative effects on your bones or joints.....